JP2890863B2 - Polarization method for block-shaped piezoelectric material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of polarizing a block-shaped piezoelectric material, and more particularly to a method of polarizing a desired degree of polarization with high accuracy.

[0002]

2. Description of the Related Art FIG. 2 shows a conventionally known piezoelectric vibrator utilizing a thickness shear vibration mode. The piezoelectric vibrator 1
It has a structure in which electrodes 3 and 4 are formed on both main surfaces of the piezoelectric substrate 2 polarized in the direction of the arrow P so as to face the front and back at the center of the piezoelectric substrate 2. This piezoelectric vibrator 1 is manufactured according to the process shown in FIG.

[0003] First, polarization electrodes 6 are formed on both main surfaces of a block-shaped piezoelectric body 5. Next, a high voltage is applied from the polarization electrodes 6 formed on both main surfaces, and polarization is performed in the thickness direction. This polarization is performed at a considerably high voltage such as tens of thousands of volts. Therefore, when the polarization is performed in the air, a discharge or the like occurs, which is dangerous. Therefore, the polarization is usually performed in a state where the piezoelectric body 5 is immersed in the insulating oil. Next, as shown in FIG. 3, the polarized piezoelectric body 5 is cut by a dicing saw to obtain a thin plate-shaped piezoelectric mother substrate 7. Further, after forming mother electrodes 3a and 4a on both main surfaces of the obtained piezoelectric mother substrate 7,
The piezoelectric vibrator 1 of FIG. 2 is obtained by cutting along the dashed line A of FIG.

[0004]

When the piezoelectric vibrator 1 is mass-produced as described above, the block-shaped piezoelectric body 5 is first polarized in the thickness direction. However, in order to obtain a predetermined degree of polarization, it was necessary to apply a high voltage of tens of thousands of volts due to the block shape of the sample, and thus it was necessary to perform a polarization treatment while immersing in insulating oil. A complicated cleaning operation for removing the insulating oil after the treatment was required.

Further, in the piezoelectric vibrator 1 obtained through the above-described manufacturing process, it is necessary that the block-like piezoelectric body 5 is uniformly and highly accurately polarized in order to make the characteristics uniform. . Also, in actual mass production, it is necessary to stably polarize a large number of block-shaped piezoelectric members 5 with high accuracy so that different block-shaped piezoelectric members 5 have the same degree of polarization.

[0006] However, in the conventional polarization method, the piezoelectric material 5 due to the variation of the piezoelectric material, the variation of the firing lot, and the like.
Inevitably had to vary in the degree of polarization. As a result, in the obtained piezoelectric vibrator 1, the degree of polarization of the piezoelectric substrate 2 varies, which is a major cause of the characteristic variation. Not only that, since the block-shaped piezoelectric body 5 has a considerable thickness and dimensions, it was polarized by applying a very high voltage of tens of thousands V as described above. In such a polarization, it is very difficult to control the degree of polarization itself, and thus it is very difficult to uniformly and accurately polarize the block-shaped piezoelectric body 5.

Accordingly, an object of the present invention is to provide a method capable of uniformly and highly accurately polarizing a block-shaped piezoelectric body by a relatively simple method.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method for polarizing a block-shaped piezoelectric body, comprising: a first polarization step of polarizing the block-shaped piezoelectric body in a desired direction to a degree higher than a desired degree of polarization; Polarization inversion by applying a voltage in the opposite direction to the polarization process of
The second polarization, which is weaker than the desired degree of polarization so as not to reach
And a voltage in the same direction as the first polarization step.
By increasing the degree of polarization Te, third to obtain the desired degree of polarization
And a polarization step.

[0009]

In the present invention, the reason why the block-shaped piezoelectric body can be highly accurately polarized to a desired degree of polarization is as follows. Generally, when polarizing or reversing the polarization of a piezoelectric body, it is necessary to apply a voltage higher than the coercive electric field. However, in the case where the polarization is performed once, the degree of polarization is reduced, and then the voltage is applied again in the first polarization direction to increase the degree of polarization, it is important that the degree of polarization can be changed with a very low voltage. Found by the inventor. This is considered to be due to the effect of the initial polarization treatment remaining. Therefore, the degree of polarization can be increased at a low voltage, and a desired degree of polarization can be obtained with high accuracy.

The polarization in the first polarization step may be polarization stronger than a desired degree of polarization. For example, the polarization may be in a saturated polarization state.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention. As the block-shaped piezoelectric body, a piezoelectric body made of Pb (TiZr) O ₃ -based ceramic and having a size of 20 mm × 30 mm × 7 mm in thickness was prepared by press molding.

As shown in FIG. 3, a polarizing electrode 6 is formed on both main surfaces of the block-shaped piezoelectric body, and a voltage of 20 kV is applied at 80 ° C. for 1 hour to perform a polarization process to obtain a saturated polarization state. Aged at a temperature of 150 ° C. for 1 hour. In this saturated polarization state, the degree of polarization ΔF for the spreading vibration mode (short-side vibration) was about 9 kHz (see FIG. 1). Next, as shown in FIG. 1, a voltage was applied to the block-shaped piezoelectric body in the saturated polarization state in a direction opposite to that of the first polarization step, so that a low polarization state was obtained. In this case, four types of block-shaped piezoelectric bodies are prepared, and the degree of polarization is ΔF = 7.0, respectively.
kHz, ΔF = 5.0 kHz, ΔF = 3.0 kHz
And ΔF = 0.1 kHz.

In order to realize the above-mentioned degree of polarization ΔF, the following method may be carried out instead of the above method. (Alternative method) A voltage of 20 kV is applied at 80 ° C. for 1 hour,
Next, after applying a reverse voltage to lower the degree of polarization,
Aging for 1 hour. According to this method, the first and second polarization treatments in the above method can be performed in a series of steps.

Next, a voltage is again applied in the forward direction to each of the four types of block-shaped piezoelectric materials in the low polarization state,
The degree of polarization was increased. In this case, when the applied voltage on the horizontal axis in FIG. 1 is x, xkV / 7 mm × 80 ° C. × 1
The test was performed under the condition of 0 minutes. Four types of block-shaped piezoelectric materials ~
In each case, the degree of polarization was increased, and eventually the state was saturated (see FIG. 1).

By the way, as is clear from the relationship between the polarization degree ΔF (kHz) and the applied voltage in FIG. 1, in the third polarization step, that is, when the polarization processing is performed so as to finally increase the polarization degree, the polarization degree − It can be seen that the applied voltage curve is considerably gentler than when the degree of polarization is reduced in the second polarization step. Therefore, in the example, for example, the degree of polarization is 5.
Polarization degree higher than 0 kHz, for example, 5.2 to 5.6 kHz
It can be seen that when trying to obtain a degree of polarization near Z, such a degree of polarization can be realized with high accuracy. In addition, for example, in the case of starting the third polarization step, the block-shaped piezoelectric body has a polarization degree of 5.0 kHz,
A relatively low voltage (800 V when trying to obtain a polarization of 5.2 kHz, 1400 V when trying to obtain a polarization of 5.4 kHz, It can be seen that the desired degree of polarization can be increased only by applying 2000 V).

When the degree of polarization is increased in the third polarization step, not only is the applied voltage increased as described above to increase the degree of polarization, but also by applying a lower applied voltage and lengthening the polarization time. It is also possible to increase the degree of polarization. That is, in the case of the above-described experimental example, as shown in FIG. 4, it is understood that the polarization degree can be more slowly increased by extending the polarization time under the condition of 1000 V × 80 ° C.
Therefore, it is understood that the degree of polarization can be controlled with higher precision by applying a lower voltage and extending the polarization time in the third polarization step.

A large number of piezoelectric vibrators shown in FIG. 2 were manufactured using the block-shaped piezoelectric material subjected to the polarization treatment as described above. FIG. 5 shows the relationship between the polarization degree ΔF of the used block-shaped piezoelectric body in the spreading vibration mode and the polarization degree Δf of the manufactured piezoelectric vibrator with respect to the thickness shear vibration of the piezoelectric substrate. In addition, the solid line B, the broken line C, and the dashed-dotted line D in FIG. 5 indicate the average values of the characteristics of a plurality of piezoelectric vibrators obtained from the block-shaped piezoelectric bodies obtained in different firing lots.
As is clear from FIG. 5, the polarization degree ΔF of the block-shaped piezoelectric material was
It can be seen that there is a similar correlation between the degree of polarization Δf of the piezoelectric substrate of the piezoelectric vibrator. Therefore, according to the present invention, it can be seen that a piezoelectric component having a desired degree of polarization can be stably supplied.

[0018]

As described above, according to the method for polarizing a block-shaped piezoelectric body of the present invention, it is possible to uniformly and accurately polarize the block-shaped piezoelectric body by applying a relatively low voltage. Become. In addition, since a low voltage can be applied in the third polarization step to perform polarization, the third polarization step can be performed in air, and thus the polarization operation can be easily performed.
Therefore, the control step of the degree of polarization, that is, the third polarization step can be automated, and the mass productivity of piezoelectric components can be drastically improved.

Further, since the block-shaped piezoelectric body can be polarized with high precision, it is possible to increase the yield rate of the piezoelectric components manufactured from the block-shaped piezoelectric body.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a polarization degree ΔF of a block-shaped piezoelectric body and an applied voltage in an example of the present invention.

FIG. 2 is a perspective view showing a piezoelectric vibrator as an example of a piezoelectric component obtained from a block-shaped piezoelectric body.

3 is a perspective view for explaining a step of obtaining the piezoelectric vibrator of FIG. 2 from a block-shaped piezoelectric body.

FIG. 4 is a diagram showing a change in the degree of polarization ΔF when a polarization time is extended by reducing an applied voltage in a third polarization step.

FIG. 5 shows the polarization degree of the block-shaped piezoelectric body ΔF and the polarization degree Δ of the piezoelectric substrate of the piezoelectric vibrator obtained from the block-shaped piezoelectric body.
It is a figure showing relation with f.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric vibrator 2 ... Piezoelectric substrate 3, 4 ... Electrode 5 ... Block-shaped piezoelectric body 6 ... Polarizing electrode 7 ... Piezoelectric mother board

Claims (1)

(57) [Claims] 1. A method of polarizing a block-shaped piezoelectric body, comprising: a first polarization step of polarizing the block-shaped piezoelectric body in a desired direction to a degree larger than a desired degree of polarization; and a reverse of the first polarization step. Voltage in the direction
A second polarization step in which polarization is weaker than a desired degree of polarization so as not to cause inversion, and applying a voltage in the same direction as the first polarization step to reduce the degree of polarization .
And a third polarization step of obtaining a desired degree of polarization by increasing the polarization degree.